Low-pressure turbine rotor

ABSTRACT

The object of the invention is to provide a low-pressure turbine rotor capable of maintaining mechanical strength characteristics, and without problems in terms of quality without increasing manufacturing costs and manufacturing days, even if high temperature steam is introduced into the low-pressure turbine. A low-pressure turbine rotor used in a steam turbine facility including a high-pressure turbine, an intermediate-pressure turbine, and a low-pressure turbine includes a member formed from 1CrMoV steel, 2.25CrMoV steel, or 10CrMoV steel arranged on a steam inlet side, and a member formed from 3.5Ni steel arranged on a steam outlet side, which are joined together by welding. Alternatively, the member arranged on the steam inlet side and the member arranged on the steam outlet side, both of which are formed from 3.5Ni steel, are joined together by welding, and the member arranged on the steam inlet side is made of low-impurity 3.5Ni steel containing, by weight %, Si: 0.1% or less, Mn: 0.1% or less, and inevitable impurities containing, by weight %, P: 0.02% or less, S: 0.02% or less, Sn: 0.02% or less, As: 0.02% or less, Sb: 0.02% or less, Al: 0.02% or less, and Cu: 0.1% or less.

TECHNICAL FIELD

The present invention relates to a low-pressure turbine rotor used in asteam turbine facility including a high-pressure turbine, anintermediate-pressure turbine, and a low-pressure turbine, andparticularly, to a low-pressure turbine rotor suitably used in a steamturbine facility in which the steam inlet temperature attains ahigh-temperature of 380° C. or higher.

BACKGROUND ART

Three methods of atomic power, thermal power, and hydraulic powergeneration, are now used as main power generation methods, and from aviewpoint of resource quantity and energy density, the three powergeneration methods are also expected to be used as main power generationmethods in the future. Especially, since thermal power generation issafe and its utility value is high as a power generation method with ahigh capacity to respond to load change, it is expected that thermalpower generation will also continue to play an important role in thepower generation field in the future.

A steam turbine facility used for coal-fired thermal power generationincluding a steam turbine, generally has a high-pressure turbine, anintermediate-pressure turbine, and a low-pressure turbine, and steam inthe range of 600° C. is used for the steam turbine facility. In such asteam turbine facility, steam in the 600° C. range supplied from aboiler is introduced into the high-pressure turbine in a high-pressureblade stage composed of blades and a vanes to rotate the high-pressureturbine to perform expansion work. Thereafter, the steam is exhaustedfrom the high-pressure turbine and is introduced into theintermediate-pressure turbine to rotate the intermediate-pressureturbine to perform expansion work, similarly to the high-pressureturbine. Further, the steam is introduced into the low-pressure turbineto perform expansion work and is exhausted and condensed to a condenser.

Generally the low-pressure turbine rotor in such a steam turbinefacility is formed from 3.5Ni steel (for example, 3.5NiCrMoV steel,etc.), and the inlet steam temperature of the low-pressure turbine wasset to 380° C. or lower that is a temperature such that 3.5Ni steel isable to maintain mechanical strength characteristics and toughness.

In the above steam turbine facility, a technique adopting a steamcondition of 630° C. or higher is recently required in order to reduceemissions of CO₂ and further improve thermal efficiency.

If steam of 630° C. or higher is introduced into the high-pressureturbine, and the same high-pressure turbine and intermediate-pressureturbine as a conventional case using steam in the 600° C. range areused, there is a possibility that the inlet steam temperature of thelow-pressure turbine may rise as high as about 400 to 430° C., greaterthan conventional, and the rotor of the low-pressure turbine is not ableto maintain its mechanical strength characteristics and toughness due tothe rise in temperature.

Especially, in the case of double-stage reheating, second-stagereheating pressure becomes low. Thus, the inlet steam temperature of thelow pressure turbine of the double-stage reheating rises higher thansingle-stage reheating, and design conditions become strict.

In order to maintain the mechanical strength characteristics andtoughness of the low-pressure turbine rotor using steam of 630° C. orhigher and formed from 3.5Ni steel, it is considered that the expansionwork amounts in the high-pressure turbine and the intermediate-pressureturbine are increased higher than ever before to reduce the steamtemperature at the inlet of the low-pressure turbine to 380° C. orlower. However, for that purpose it is necessary to increase the numberof blade stages of the high-pressure turbine and theintermediate-pressure turbine, and there is a problem that the wholeturbine becomes enlarged.

Thus, Patent Document 1 disclosed a low-pressure turbine rotor capableof reducing the content of impurities contained in 3.5Ni steel whichconstitutes the low-pressure turbine rotor, and limiting the content toa minute amount, thereby suppressing changes in the structure of themetal which induces embrittlement over time, such as grain boundarysegregation of impurity elements caused by heating, and stablyperforming operations even if steam of 380° C. or higher is introduced.

Stricter impurity management than ever before is required in thetechnique disclosed in Patent Document 1. However, especially, thelow-pressure turbine rotor is large-sized. Therefore, when an integrallow-pressure turbine rotor is used in the technique disclosed in PatentDocument 1, a problem occurs in that reliability in terms of quality ofa turbine rotor to be manufactured remains unstable such that costincreases, manufacturing days increase and delivery dates becomedelayed, and the content of impurities exceeds a criteria, for example,due to dispersion.

PRIOR ART DOCUMENT Patent Document

[Patent Document 1] Japanese Patent Application Laid-Open No.2006-170006

SUMMARY OF THE INVENTION

Accordingly, the invention was made in view of the problems of theconventional technique, and the object thereof is to provide alow-pressure turbine rotor capable of maintaining mechanical strengthcharacteristics, and without problems in terms of quality withoutincreasing manufacturing costs and manufacturing days, even if hightemperature steam is introduced into the low-pressure turbine.

In order to solve the above problem, the present invention provides alow-pressure turbine rotor used in a steam turbine facility including ahigh-pressure turbine, an intermediate-pressure turbine, and alow-pressure turbine. The turbine rotor includes a member formed from1CrMoV steel (hereinafter referred to as 1Cr steel), 2.25CrMoV steel(hereinafter referred to as 2.25Cr steel), or 10CrMoV steel (hereinafterreferred to as 10Cr steel) arranged on a steam inlet side, and a memberformed from 3.5Ni steel arranged on a steam outlet side, which arejoined together by welding.

Since 1Cr steel, 2.25Cr steel, and 10Cr steel are materials which haveconventionally been used for high-pressure turbine rotors orintermediate-pressure turbine rotors, the material management methodsare established, and also easily available. Moreover, the abovematerials have a more excellent high-temperature resistance than 3.5Nisteel.

Additionally, 3.5Ni steel has stress corrosion cracking (SCC)susceptibility lower than 1Cr steel and 2.25Cr steel. Additionally, 10Crsteel is more expensive than 3.5Ni steel.

Thus, steam inlet side into which high-temperature steam is introducedincludes a member formed from 1Cr steel, 2.25Cr steel, or 10Cr steel,and steam outlet side in which a flow passage (blade length) increasesand higher strength is required includes a member formed from 3.5Nisteel, whereby it is possible to form a low-pressure turbine rotor whichis excellent against high-temperature and stress corrosion cracking, andeven if high-temperature steam is introduced, it is possible to maintainits mechanical strength characteristics and toughness.

Moreover, although 3.5Ni steel and 1Cr steel are almost the same fromthe viewpoint of embrittlement, 2.25Cr steel and 10Cr steel are superiorto 3.5Ni steel. Accordingly, if a member made of 1Cr steel is used forthe steam inlet side, the embrittlement susceptibility of the wholelow-pressure turbine rotor is almost the same as the conventionallow-pressure turbine rotor the entirety of which is made of 3.5Ni steel.However, if a member made of 2.25Cr steel or 10Cr steel is used for thesteam inlet side, the embrittlement susceptibility of the wholelow-pressure turbine rotor is superior to the conventional low-pressureturbine rotor the entirety of which is made of 3.5Ni steel. Therefore,the member on the steel inlet side is more preferably formed from 2.25Crsteel or 10Cr steel.

Additionally, there is provided a low-pressure turbine rotor used in asteam turbine facility including a high-pressure turbine, anintermediate-pressure turbine, and a low-pressure turbine. The turbinerotor includes a member arranged on a steam inlet side and a memberarranged on a steam outlet side, which are joined together by welding,both the members are formed from 3.5Ni steel, and the member arranged onthe steam inlet side is formed from low-impurity 3.5Ni steel.

Additionally, the low-impurity 3.5Ni steel arranged on the steam inletside contains, by weight %, Si: 0.1% or less, Mn: 0.1% or less, andinevitable impurities, by weight %, containing P: 0.02% or less, S:0.02% or less, Sn: 0.02% or less, As: 0.02% or less, Sb: 0.02% or less,Al: 0.02% or less, and Cu: 0.1% or less.

By using the member made of 3.5Ni steel the impurity content of which isreduced and limited to a minute amount for the steam inlet side intowhich high-temperature steam is introduced, it is possible to suppresschanges in the metal structure which induce embrittlement over time,such as grain boundary segregation of impurity elements caused byheating, and even if steam of 380° C. or higher is introduced, it ispossible to stably perform operation.

Moreover, by using a member made of 3.5Ni steel the impurity content ofwhich is reduced not for the whole rotor but for the steam inlet sideinto which high-temperature steam is introduced, it is possible tofabricate a low-pressure turbine rotor in which an increase inmanufacturing costs and manufacturing days is suppressed, and theuncertainness in reliability in terms of quality is also small.

Additionally, the low-pressure turbine rotor is used in a steam turbinefacility where the inlet steam temperature of the low-pressure turbineis 380° C. or higher,

a region where the temperature of the steam passing through thelow-pressure turbine becomes 380° C. or higher includes the memberarranged on the steam inlet side, and a region where the temperature ofthe steam passing through the low-pressure turbine is less than 380° C.includes the member arranged on the steam outlet side.

The normal 3.5Ni steel has a high possibility of inducing embrittlementover time, such as grain boundary segregation of impurity elements, ifsteam temperature becomes 380° C. or higher. Thus, a region where steamtemperature becomes 380° C. or higher includes the member arranged onthe steam inlet side, and a region where steam temperature is less than380° C. includes the member arranged on the steam outlet side, wherebythe normal 3.5Ni steel does not contact steam of 380° C. or higher, andit is possible to suppress embrittlement of a member formed from the3.5Ni steel arranged on the steam outlet side.

The low-pressure turbine rotor is used in a steam turbine facility wherethe inlet steam temperature of at least one of the high-pressure turbineand the intermediate-pressure turbine is 630° C. or higher.

Thereby, the high-pressure turbine and the intermediate-pressure turbineare not enlarged, it is possible to reduce emissions of CO₂ from thesteam turbine facility, and it is possible to improve the thermalefficiency of the steam turbine facility.

As described above, according to the invention, it is possible toprovide a low-pressure turbine rotor capable of maintaining mechanicalstrength characteristics, and without problems in terms of qualitywithout increasing manufacturing costs and manufacturing days, even ifhigh temperature steam is introduced into the low-pressure turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating the configuration of a steam turbine powergeneration facility in Embodiment 1.

FIG. 2 is a plan view schematically illustrating the configuration of alow-pressure turbine rotor in Embodiment 1.

FIG. 3 is a plan view schematically illustrating the configuration of alow-pressure turbine rotor in Embodiment 2.

FIG. 4 is a graph illustrating the embrittlement factors of 1Cr steel,2.25Cr steel, 10Cr steel, and 3.5Ni steel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred examples of the invention will be illustratively describedbelow in detail with reference to the drawings. Here, the dimensions,materials, shapes, relative arrangements, etc. of component partsdescribed in this example are not meant to limit the scope of theinvention, but are merely simple explanatory examples, as long as thereis no specific description of limitations.

Example 1

FIG. 1 is a view illustrating the configuration of a steam turbine powergeneration facility in Embodiment 1.

With reference to FIG. 1, a power generation facility composed of asteam turbine facility using a low-pressure turbine rotor of theinvention will be described.

In addition, FIG. 1 is an example of single-stage reheating, and theinvention is also applied to implementation of double-stage reheatingand a high temperature rise (630° C. or higher) only by reheating, andis not particularly limited.

The steam turbine power generation facility 10 illustrated in FIG. 1mainly includes a high-pressure turbine 14, an intermediate-pressureturbine 12, a low-pressure turbine 16, a power generator 18, a condenser20, and a boiler 24. The steam passes through in order of a boiler 24, amain steam pipe 26, the high-pressure turbine 14, a low-temperaturereheat pipe 28, the boiler 24, the high-temperature reheat pipe 30, theintermediate-pressure turbine 12, a crossover pipe 32, the low-pressureturbine 16, the condenser 20, a water feed pump 22, and the boiler 24.

The steam overheated to 630° C. or higher in the boiler 24 is introducedinto the high-pressure turbine 14 through the main steam pipe 26. Thesteam introduced into the high-pressure turbine 14 is exhausted and isreturned to the boiler 24 through the low-temperature reheat pipe 28after having performed expansion work. The steam returned to the boiler24 is reheated in the boiler 24 and turned into steam of 630° C. orhigher, and is sent to the intermediate-pressure turbine 12 through thehigh-temperature reheat pipe 30. The steam introduced into theintermediate-pressure turbine 12 is exhausted, is turned into steam ofabout 400 to 430° C., and is sent to the low-pressure turbine 16 throughthe crossover pipe 32 after having performed expansion work. The steamintroduced into the low-pressure turbine 16 is exhausted and is sent tothe condenser 20 after having performed expansion work. The steam sentto the condenser 20 is condensed in the condenser 20, is increased inpressure in the water feed pump 22, and is returned to the boiler 24.The power generator 18 is rotationally driven by the expansion work ofeach turbine to generate power.

FIG. 2 is a plan view schematically illustrating the configuration ofthe rotor used for the low-pressure turbine 16 in Embodiment 1.

The low-pressure turbine rotor used for the steam turbine powergeneration facility as mentioned above will be described with referenceto FIG. 2.

(Configuration)

First, the configuration of the rotor according to this example used forthe low-pressure turbine 16 into which steam of about 400 to 430° C. isintroduced will be described with reference to FIG. 2.

As illustrated in FIG. 2, the low-pressure turbine rotor 16A includesone member (hereinafter referred to as chrome steel portion) 16 a madeof 1Cr steel, 2.25Cr steel, or 10Cr steel, and two members (hereinafterreferred to as normal 3.5Ni steel portions) 16 b and 16 c made of 3.5Nisteel.

The chrome steel portion 16 a is joined to the normal 3.5Ni steelportions 16 b and 16 c, respectively, by welding at both ends thereof,thereby forming the low-pressure turbine rotor 16A integrated in orderof the normal 3.5Ni steel portion 16 b, the chrome steel portion 16 a,and the normal 3.5Ni steel portion 16 c from one end.

Additionally, the chrome steel portion 16 a is arranged at a positionexposed to steam of 380° C. or higher, and the normal 3.5Ni steelportions 16 b and 16 c are arranged at positions exposed to steam ofless than 380° C.

(Materials)

Next, the materials of the chrome steel portion 16 a and the 3.5Ni steelportions 16 b and 16 c which constitutes the low-pressure turbine rotor16A, will be described.

(A) Chrome Steel Portion

The chrome steel portion is formed from 1Cr steel, 2.25Cr, or 10Cr steelwhich has excellent in high-temperature resistance, and is easilyavailable.

The 1Cr steel may include, for example, a material having compositioncontaining, by weight %, C: 0.2 to 0.4%, Si: 0.35% or less, Mn: 1.5% orless, Ni: 2.0% or less, Cr: 0.5 to 1.5%, Mo: 0.5 to 1.5%, V: 0.2 to0.3%, and the balance: Fe with inevitable impurities.

The 2.25Cr Steel may include, for example, a material having compositioncontaining, by weight %, C: 0.2 to 0.35%, Si: 0.35% or less, Mn: 1.5% orless, Ni: 0.2 to 2.0%, Cr: 1.5 to 3.0%, Mo: 0.9 to 1.5%, V: 0.2 to 0.3%,and the balance: Fe with inevitable impurities.

The 10Cr steel may include, for example, a material having compositioncontaining, by weight %, C: 0.05 to 0.4%, Si: 0.35% or less, Mn: 2.0% orless, Ni: 3.0% or less, Cr: 7 to 13%, Mo: 0.1 to 3.0%, V: 0.01 to 0.5%,N: 0.01 to 0.1%, Nb: 0.01 to 0.2%, and the balance: Fe with inevitableimpurities.

The 10Cr steel of another example may include, for example, a materialhaving composition containing, by weight %, C: 0.05 to 0.4%, Si: 0.35%or less, Mn: 2.0% or less, Ni: 7.0% or less, Cr: 8 to 15%, Mo: 0.1 to3.0%, V: 0.01 to 0.5%, N: 0.01 to 0.1%, Nb: 0.2% or less, and thebalance: Fe with inevitable impurities.

FIG. 4 is a graph illustrating the embrittlement factor of 1Cr steel,2.25Cr steel, 10Cr steel, and 3.5Ni steel. The ordinate axis representsembrittlement factors (ΔFATT), and values used as the index of theeasiness of embrittlement. As the numeric value of this factor ishigher, susceptibility to embrittlement is higher and embrittlement iseasier. The abscissa axis represents J-Factors and values used as theindex of the concentration of impurities. As is clear from FIG. 4,materials easily embrittle as the impurity concentration increases.Moreover, 1Cr steel and 3.5Ni steel have almost the same embrittlementfactors, the embrittlement factor of 2.25Cr steel is lower than that,and the embrittlement factor of 10Cr steel is lower still.

Accordingly, if a member made of 1Cr steel is used for the chrome steelportion 16 a, it can be said that the embrittlement susceptibility ofthe whole low-pressure turbine rotor is almost the same as theconventional low-pressure turbine rotor in which the whole rotor is madeof 3.5Ni steel. However, if members made of 2.25Cr steel or 10Cr steelare used for the chrome steel portions 16 b and 16 c, it can be saidthat the embrittlement susceptibility of the whole low-pressure turbinerotor is lower than the conventional low-pressure turbine rotor in whichthe whole rotor is made of 3.5Ni steel, i.e., the turbine rotor hardlyembrittles. Therefore, the chrome steel portion 16 a is more preferablyformed from 2.25Cr steel or 10Cr steel.

(B) Normal 3.5Ni Steel Portion

The 3.5Ni steel may include, for example, a material having compositioncontaining, by weight %, C: 0.4% or less, Si: 0.35% or less, Mn: 1.0% orless, Cr: 1.0 to 2.5%, V: 0.01 to 0.3%, Mo: 0.1 to 1.5%, Ni: 3.0 to4.5%, and the balance: Fe with inevitable impurities.

(Manufacturing Method)

Joining is made by welded portions between the chrome steel portion 16 aand the normal 3.5Ni steel portions 16 b and 16 c by welding.

Although the method of the welding is not particularly limited if thewelded portions are able to withstand the operational conditions of thelow-pressure turbine, it is possible to include a general welding methodof supplying a weld wire to an arc generated by a welding torch as anexample as a filler.

For example, a narrow groove welding joint, etc. is adopted as the shapeof the welded portions. In welding, a filler supplied as a weld wire bymelting caused by an arc is laminated for every single pass, and thefiller is filled into the narrow groove welding joint, thereby joiningtogether the chrome steel portion 16 a and the normal 3.5N1 steelportions 16 b and 16 c. The 3.5Ni steel that is the same material as thenormal 3.5Ni steel portion is used as the filler.

The following effects are obtained by using the low-pressure turbinerotor described above.

Since 1Cr steel, 2.25Cr steel, and 10Cr steel are materials which haveconventionally been used for high-pressure turbine rotors orintermediate-pressure turbine rotors, the materials management methodsare established, and also easily available. Moreover, the abovematerials have more excellent high-temperature resistance than 3.5Nisteel. Additionally, 3.5Ni steel has stress corrosion cracking (SCC)susceptibility lower than 1Cr steel, 2.25Cr steel, and 10Cr steel. Thus,steam inlet side into which high-temperature steam is introducedincludes a member formed from 1Cr steel, 2.25Cr steel, or 10Cr steel,and steam outlet side in which a flow passage diameter (blade diameter)increases and higher strength is required includes a member formed from3.5Ni steel, whereby it is possible to form a low-pressure turbine rotorwhich is excellent against high-temperature and stress corrosioncracking, and even if high-temperature steam is introduced, it ispossible to maintain its mechanical strength characteristics.

Additionally, the normal 3.5Ni steel has a high possibility of inducingembrittlement over time, such as grain boundary segregation of impurityelements, if the steam temperature becomes 380° C. or higher. Thus, aregion where the steam temperature becomes 380° C. or higher includes amember arranged on the steam inlet side, and a region where steamtemperature is less than 380° C. includes a member arranged on the steamoutlet side, whereby the normal 3.5Ni steel does not contact the steamof 380° C. or higher, and it is possible to suppress embrittlement of amember formed from the 3.5Ni steel arranged on the steam outlet side.

Moreover, since it is possible to maintain the mechanical strengthcharacteristics of the low-pressure turbine rotor even if the inletsteam temperature of the low-pressure turbine is made higher than everbefore, it is possible to use steam of 630° C. or higher withoutenlarging the high-pressure turbine and the intermediate-pressureturbine, it is possible to reduce emissions of CO₂ from the steamturbine facility, and it is possible to improve the thermal efficiencyof the steam turbine facility.

Example 2 Configuration

In Embodiment 2, a low-pressure turbine rotor 16B of another form willbe described.

In Embodiment 2, as illustrated in FIG. 3, the low-pressure turbinerotor 16B includes one member (referred to as a low-impurity 3.5Ni steelportion) 16 d made of low-impurity 3.5Ni steel with little impuritycontent, and the normal 3.5Ni steel portions 16 b and 16 c.

That is, Embodiment 2 is a form in which the low-impurity 3.5Ni steelportion 16 d is adopted instead of the chrome steel portion 16 a of thelow-pressure turbine rotor with the form of Embodiment 1 illustrated inFIG. 2. Hereinafter, since configurations other than the low-impurity3.5Ni steel portion 16 d are the same as those of Embodiment 1, thedescription thereof is omitted.

Additionally, the low-impurity 3.5Ni steel portion 16 d is arranged at aposition exposed to steam of 380° C. or higher, and the normal 3.5Nisteel portions 16 b and 16 c are arranged at positions exposed to steamof less than 380° C.

(Materials)

The materials of the low-impurity 3.5Ni steel portion 16 d will bedescribed.

The low-impurity 3.5Ni steel portion 16 d is formed from a 3.5Ni steelportion with little impurity content. The low-impurity 3.5Ni steelportion 16 d may include, for example, a material having compositioncontaining, by weight %, C: 0.4% or less, Si: 0.1% or less, Mn: 0.1% orless, Cr: 1.0 to 2.5%, V: 0.01 to 0.3%, Mo: 0.1 to 1.5%, Ni: 3.0 to4.5%, and the balance: Fe with inevitable impurities, and the inevitableimpurities contain, by weight %, P: 0.02% or less, S: 0.02% or less, Sn:0.02% or less, As: 0.02% or less, Sb: 0.02% or less, Al: 0.02% or less,and Cu: 0.1% or less.

(Manufacturing Method)

Joining is made by welded portions between the low-impurity 3.5Ni steelportion 16 d and the normal 3.5Ni steel portions 16 b and 16 c bywelding.

As illustrated in FIG. 4, as the 3.5Ni steel has lower impurityconcentration, embrittlement susceptibility is lower and embrittlementhardly occurs.

Accordingly, by using the member 16 d made of low-impurity 3.5Ni steelthe impurity content of which is reduced and limited to a minute amountfor the steam inlet side into which high-temperature steam isintroduced, it is possible to suppress changes in metal structure whichinduces embrittlement over time, such as grain boundary segregation ofimpurity elements caused by heating, and even if the steam of 380° C. orhigher is introduced, it is possible to stably perform operation.

Moreover, by using a member made of 3.5Ni steel the impurity content ofwhich is reduced not for the whole rotor but for the steam inlet sideinto which high-temperature steam is introduced, it is possible tofabricate a low-pressure turbine rotor in which an increase inmanufacturing costs and manufacturing days is suppressed, and theinstability of reliability in terms of quality is also small.

Additionally, the normal 3.5Ni steel has a high possibility of inducingembrittlement over time, such as grain boundary segregation of impurityelements, if steam temperature becomes 380° C. or higher. Thus, a regionwhere steam temperature becomes 380° C. or higher includes the memberarranged on the steam inlet side, and a region where steam temperatureis less than 380° C. includes the member arranged on the steam outletside, whereby the normal 3.5Ni steel does not contact the steam of 380°C. or higher, and it is possible to suppress embrittlement of a memberformed from the 3.5Ni steel arranged on the steam outlet side.

Moreover, since it is possible to maintain the mechanical strengthcharacteristics of the low-pressure turbine rotor even if the inletsteam temperature of the low-pressure turbine is made higher than everbefore, it is possible to use the steam of 630° C. or higher withoutenlarging the high-pressure turbine and the intermediate-pressureturbine, it is possible to reduce emissions of CO₂ from the steamturbine facility, and it is possible to improve the thermal efficiencyof the steam turbine facility.

INDUSTRIAL APPLICABILITY

It is possible to utilize the invention as a low-pressure turbine rotorcapable of maintaining its mechanical strength characteristics, andwithout problems in terms of quality, without increasing manufacturingcosts and manufacturing days, even if high temperature steam isintroduced into the low-pressure turbine.

1. A low-pressure turbine rotor used in a steam turbine facilityincluding a high-pressure turbine, an intermediate-pressure turbine, anda low-pressure turbine, the turbine rotor comprising a member formedfrom 1CrMoV steel, 2.25CrMoV steel, or 10CrMoV steel arranged on a steaminlet side, and a member formed from 3.5Ni steel arranged on a steamoutlet side, which are joined together by welding.
 2. A low-pressureturbine rotor used in a steam turbine facility including a high-pressureturbine, an intermediate-pressure turbine, and a low-pressure turbine,the turbine rotor comprising a member arranged on a steam inlet side anda member arranged on a steam outlet side, which are joined together bywelding, both the members being formed from 3.5Ni steel, and the memberarranged on the steam inlet side being formed from low-impurity 3.5Nisteel.
 3. The low-pressure turbine rotor according to claim 2, whereinthe low-impurity 3.5Ni steel arranged on the steam inlet side contains,by weight %, Si: 0.1% or less, Mn: 0.1% or less, and inevitableimpurities, by weight %, containing P: 0.02% or less, S: 0.02% or less,Sn: 0.02% or less, As: 0.02% or less, Sb: 0.02% or less, Al: 0.02% orless, and Cu: 0.1% or less.
 4. The low-pressure turbine rotor accordingto claim 1, wherein the low-pressure turbine rotor is used in a steamturbine facility where the inlet steam temperature of the low-pressureturbine is 380° C. or higher, a region where the temperature of thesteam passing through the low-pressure turbine attains temperatures of380° C. or higher includes the member arranged on the steam inlet side,and a region where the temperature of the steam passing through thelow-pressure turbine is less than 380° C. includes the member arrangedon the steam outlet side.
 5. The low-pressure turbine rotor according toclaim 1, wherein the low-pressure turbine rotor is used in a steamturbine facility where the inlet steam temperature of at least one ofthe high-pressure turbine and the intermediate-pressure turbine is 630°C. or higher.
 6. The low-pressure turbine rotor according to claim 2,wherein the low-pressure turbine rotor is used in a steam turbinefacility where the inlet steam temperature of the low-pressure turbineis 380° C. or higher, a region where the temperature of the steampassing through the low-pressure turbine attains temperatures of 380° C.or higher includes the member arranged on the steam inlet side, and aregion where the temperature of the steam passing through thelow-pressure turbine is less than 380° C. includes the member arrangedon the steam outlet side.
 7. The low-pressure turbine rotor according toclaim 2, wherein the low-pressure turbine rotor is used in a steamturbine facility where the inlet steam temperature of at least one ofthe high-pressure turbine and the intermediate-pressure turbine is 630°C. or higher.
 8. The low-pressure turbine rotor according to claim 3,wherein the low-pressure turbine rotor is used in a steam turbinefacility where the inlet steam temperature of at least one of thehigh-pressure turbine and the intermediate-pressure turbine is 630° C.or higher.